Heretofore, many studies have been made assessing the quality of electrical power available commercially and its effect on driving modern, sophisticated, high speed computer systems. One of the most comprehensive and impartial studies is that of an IEEE published Bell Telephone Laboratories study entitled, "The Quality of U.S. Commercial AC Power". The presentation of this study was made in Washington, D.C. during a Telecommunications and Energy conference held October 3-6, 1986. The presentation was made by Dr. Marvin Goldstein and Mr. Paul Speranza.
In this report, the authors gathered data from 24 A T & T Long Line, Western Electric and Bell Operating company sites in twelve different states. The data spanned 270 total months of power monitoring for the purpose of reducing or eliminating computer downtime for the Bell System through the selection of appropriate, cost-effective, power conditioning equipment. The following power problems, listed as a percent of total number of events, were the findings of this study:
Sags--87% PA1 Impulses (Noise) 7.4% PA1 Power failures 4.7% PA1 Surges 0.7%
Further data from the aforementioned report with respect to the duration of power sags is illustrated in the following table: